The Plant Body

Themes in plant form



  • Plants gather materials to grow
    • soil
    • atmosphere
    • materials can be limiting


  • Above and belowground body plan

Themes in plant form



  • Plants gather materials to grow
    • soil
    • atmosphere
    • materials can be limiting


  • Above and belowground body plan


  • Plants exhibit indeterminate growth
    • “foragers”
    • diversity of size & shape

Plants do all this without moving!





  • Mostly defined by their total inability to move


  • Is this a good thing or a bad thing?


  • Their Darwinian struggle for growth, survival and reproduction in very different arenas has resulted in an extremely wide variety of form and function (Diaz et al 2016)

Dermal (1) tissue (aka ‘Skin’)




  • Outer layer in young/non-woody plants = epidermis
    • single layer of flattened cells


  • Woody plants epidermis cracks and is replaced
    • occurs from ____________
    • new layer is called periderm
    • whole thing called ‘bark’

Wine cork = periderm from Quercus suber

Epidermal cells secrete ‘cutin’




  • Wax-like substances that forms the ‘cuticle’
    • prevents evaporative water loss
    • makes the plant water proof


  • Often thick enough to make leaf shiny
    • succulents & tropical plants

Epidermal cells secrete ‘cutin’



  • Wax-like substances that forms the ‘cuticle’
    • prevents evaporative water loss
    • makes the plant water proof


  • Often thick enough to make leaf shiny
    • succulents & tropical plants


  • Trichomes may also be present on epidermis
    • hairs (sometimes glandular)

Stomata are scattered within leaf epidermis





  • Pores that allow gas exchange
    • CO2, O2, water vapor


  • Essential since plant is ‘water proof’


  • Pair of guard cells shrink/swell to open/close
    • much more later…

How stomata work…

Ground (2) Tissues make up bulk of plant organs


  • Parenchyma = thin walled & most versatile
    • photosynthetic cells in green tissues
    • storage cells in other organs


  • Collencyhma = primary support cells
    • elongated & thick
    • living
    • ‘strings’ in celery


  • Schlerenchyma = mechanical support & protection
    • elongate & very thick
    • dead @ maturity
    • used to make cloth and rope

Parenchyma cells: living, dividing with metabolic function

Collenchyma (flexible) & Sclerenchyma (rigid) for support

Vascular (3) Tissues



  • Conducting tissues in plants
    • visible in leaves = veins!


  • Two tissues systems allow unrestricted movement of materials
    • created from apical and lateral meristems


  • Xylem = water and minerals from roots upward


  • Phloem = organic materials from source leaf to rest of plant

Pipe Theory works to visual continuum

Tracheids and vessels are conducting xylem cells



  • Both are dead at maturity, with just cell walls


  • Tracheids = long, thin & tapered
    • many pits in cell walls
    • pits are not holes


  • Vessels = short, wide & end to end
    • made pits in cells walls
    • unique to angiosperms

Sieve tube members make up phloem



  • Living cells with only primary cell wall
    • nucleus/organelles eventually disappear


  • Sieve plates = end walls with large pores


  • Each seive tube has a companion cell
    • developmentally tied together
    • lots of plasmodesmata connect 2 cells
    • loads and unloads

Vascular tissues often wrapped in bundle sheath cells

Plant organs are so easy: Stems, roots & leaves

  • Roots: tap and fibrous root systems
    • tap = one large root with small branches
    • fibrous = no central main root (grasses)


  • Stems: mostly ground tissue
    • mostly xylem in woody plants
    • inner cambium = xylem = tree ring
    • when tree grows quick = xylem are large


  • Leaves: photosynthetic machines
    • flat blade (mostly)
    • many shapes and sizes


  • Flower = modified ‘shoot’

Test yourself….this image is not a leaf….

Test yourself….this image is a leaf….